Method and Device for Transmission of Signals in a GSM System

ABSTRACT

Methods and devices for transmitting a burst of signals in a cellular radio system supporting data transmission using EGPRS/EGPRS2 are provided. The transmission involves providing additional symbols in the EGPRS/EGPRS2 burst thereby forming a long burst and pulse shaping the long burst to form a long baseband signal whose duration exceeds the duration of one EGPRS/EGPRS2 time slot. The long baseband signal is then shortened to a shortened burst having the duration of an EGPRS/EGPRS2 time slot wherein the shortened burst fulfills the same spectrum mask requirement as the EGPRS/EGPRS2 burst, which can be transmitted.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/314,666, filed Mar. 17, 2010 and incorporated herein by referencein its entirety.

TECHNICAL FIELD

The present invention relates to a method and a device for transmittingsignals in a GSM system.

BACKGROUND

Despite the fact that Global System for Mobile Communication (GSM)networks have been commercially deployed for almost two decades,interest on the continued improvement of the GSM/Enhanced Data rates forGSM Evolution (EDGE) technology has not dwindled. Network equipmentmanufacturers, mobile equipment manufacturers and telecom operatorscontinue to develop the GSM system further. Improvements to thehardware/spectral efficiencies for both voice and packet data servicesare being actively sought. To this end, precoded EGPRS/EGPRS phase 2(EGPRS2) has been proposed. Precoding involves transformation of thesymbol sequence using some suitable transform. Typically a FourierTransformation is used. FIG. 1 gives a high level view of precodedEGPRS/EGPRS2. The blocks within the dashed box in FIG. 1 will now bedescribed. After burst formatting, the bit sequence (b_(n)) has thefollowing structure.

$\begin{matrix}\left( {\underset{\underset{guard}{}}{b_{1},\ldots \mspace{14mu},b_{\alpha}},\underset{\underset{tail}{}}{b_{\alpha + 1},\ldots \mspace{14mu},b_{\beta}},\underset{\underset{data}{}}{b_{\beta + 1},\ldots \mspace{14mu},b_{\gamma}},\underset{\underset{training}{}}{b_{\gamma + 1},\ldots \mspace{14mu},b_{\delta}},\underset{\underset{data}{}}{b_{\delta + 1},\ldots \mspace{14mu},b_{ɛ}},\underset{\underset{tail}{}}{b_{ɛ + 1},\ldots \mspace{14mu},b_{\phi}},\underset{\underset{guard}{}}{b_{\phi + 1},\ldots \mspace{14mu},b_{\varphi}}} \right) & (1)\end{matrix}$

These bits are mapped to symbols drawn from a Phase Shift Keying(PSK)/Quadrature Amplitude Modulation (QAM) symbol constellation. Theletters s,x,t,g will be used to denote PSK/QAM symbols that carrytraining, payload, tail or guard bits respectively. Thus,

(b₁, . . . , b_(α), b_(φ+1), . . . , b_(φ))→{right arrow over (g)}=(g₁,. . . , g_(η)) (guard)

(b_(α+1), . . . , b_(β), b_(ε+1), . . . , b_(φ))→{right arrow over(t)}=(t₁, . . . , t_(ν)) (tail)

(b_(β+1), . . . , b_(γ), b_(δ+1), . . . , b_(ε))→{right arrow over(x)}=(x₁, . . . , x_(D)) (payload)

(b_(γ+1), . . . , b_(δ))→{right arrow over (s)}=(s₁, . . . , s_(N) _(tr)) (training symbols),

where η is the total number of guard symbols, v is the total number oftail symbols, D is the total number of payload symbols and N_(tr) is thenumber of training symbols. The total number of payload plus trainingsymbols is N=D+N_(tr) and the total number of symbols in the burst isK=N+η+v.

The output of the symbol mapping block is the sequence of symbols

$\begin{matrix}{\left\lbrack {c_{1},\ldots \mspace{14mu},c_{K}} \right\rbrack \overset{def}{=}{\left\lbrack {\overset{->}{g},\overset{->}{t},\overset{->}{x},\overset{->}{d}} \right\rbrack.}} & (2)\end{matrix}$

It is convenient to intercalate the training symbols and the payloadsymbols for synchronization and channel estimation purposes. A vector{right arrow over (z)} of length N is constructed from the payload{right arrow over (x)} and training symbols {right arrow over (s)}accordingly.

$\begin{matrix}{\overset{->}{z} = {\left\lbrack {z_{1},\ldots \mspace{14mu},z_{N}} \right\rbrack^{T}\overset{def}{=}{\left. \left\lbrack {x_{1},\ldots \mspace{14mu},s_{1},\ldots \mspace{14mu},x_{p},s_{m},\ldots \mspace{14mu},s_{N_{tr}},\ldots \mspace{14mu},x_{D}} \right\rbrack \mspace{250mu}\updownarrow\mspace{70mu}\updownarrow\mspace{115mu}\updownarrow\updownarrow\mspace{85mu}\updownarrow \mspace{239mu} {k(1)} \right.\mspace{14mu} \ldots \mspace{14mu} {n(1)}\mspace{14mu} \ldots \mspace{14mu} {k(p)}\mspace{14mu} {n(m)}\mspace{45mu} {n\left( N_{tr} \right)}\mspace{50mu} {k(D)}}}} & (3)\end{matrix}$

The location of the training symbols is given by the indices(n(m))_(m=1) ^(N) ^(tr) . Likewise, the location of the payload symbolsis given by (k(m))_(m=1) ^(D). That is, z_(n(p))=s_(p) andz_(k(p))=x_(p). The location of the training symbols should be chosencarefully as it has a large impact on the receiver performance. DiscreteFourier Transform (DFT)-precoding is applied to {right arrow over (z)}to form a new sequence of complex numbers {right arrow over (Z)} asfollows. Let W be the Fourier transform matrix of size N×N whose entryin the m-th row and i-th column is

${W_{m,i}\overset{def}{=}{\frac{1}{\sqrt{N}}{\exp \left( {{- j}\; 2{\pi \left( {m - 1} \right)}{\left( {i - 1} \right)/N}} \right)}}},$

for 1≦m,i≦N. The pre-coding operation is {right arrow over(Z)}=W^(H)·{right arrow over (z)}.

Multiplication by the matrix W^(H) can be implemented efficiently usingthe fast Fourier transform. Next, an integer L≧0 is chosen and the lastL terms in {right arrow over (Z)} are appended at the beginning of{right arrow over (Z)} to form a new vector {right arrow over (Z)}^(P).In other words, a cyclic prefix of length L is added. For example thevalues L=0 (no prefix) or L=5 (typical GSM channel length) may be used.

Using vector notation, the precoded symbols with the cyclic prefix addedare

$\begin{matrix}{{\overset{->}{Z}}^{P} = \left\lbrack {Z_{1}^{P},\ldots \mspace{14mu},Z_{N + L}^{P}} \right\rbrack} \\{\overset{def}{=}{\left\lbrack {Z_{N - L},Z_{N - L + 1},\ldots \mspace{14mu},Z_{N},Z_{1},Z_{2},\ldots \mspace{14mu},Z_{N}} \right\rbrack.}}\end{matrix}$

The output of the vector precoding (IDFT) block is the sequence ofcomplex numbers

$\begin{matrix}{\left\lbrack {d_{1}, d_{2}, \ldots \mspace{14mu}, d_{K}} \right\rbrack \overset{def}{=}{\left\lbrack {\underset{\underset{guard}{}}{{g_{1},\ldots}\mspace{14mu}}, \underset{\underset{tail}{}}{{t_{1},\ldots}\mspace{14mu}}, \underset{\underset{{payload} + {pilots}}{}}{Z_{1}^{P},Z_{2}^{P},\ldots \mspace{14mu},Z_{N + L}^{P}}, \underset{\underset{tail}{}}{\ldots \mspace{14mu},t_{v}}, \underset{\underset{guard}{}}{\ldots \mspace{14mu},g_{\eta}}} \right\rbrack .}} & (4)\end{matrix}$

This sequence is pulse shaped to obtain the baseband signal, as follows.

$\begin{matrix}{{{y(t)} = {\sum\limits_{n}{d_{n} \cdot {p\left( {t - {nT} + \phi} \right)}}}},{0 \leq t \leq {\tau.}}} & (5)\end{matrix}$

Here ρ is the pulse shaping filter, T is the symbol period (in seconds),φ is the phase and τ is the duration of the burst (in seconds). Finally,the pulse shaped signal (5) is sent to the Radio frequency (RF)modulator.

In order to make precoded EGPRS backwards compatible with EGPRS/EGPRS2,the linearized GMSK pulse shaping filter is used, see 3GPP TS 45.004Modulation. This is a partial response pulse, which introduces asignificant amount of intersymbol interference (ISI) in the transmittedsignal. Therefore, the length L of the cyclic prefix must be chosenlarge enough to cover not only the time dispersion in the radio channeland the receive filtering but also the large time dispersion introducedby the pulse shaping filter. This entails a larger overhead andtherefore a loss of bandwidth. Furthermore, due to backwardcompatibility, the size N of the IDFT is not a highly composite number.Even though there are efficient Inverse Fast Fourier Transform (IFFT)algorithms for any size, the algorithms for highly composite lengths aremuch faster. Fast, highly efficient IFFT's are desirable for backwardcompatibility with legacy base station hardware, and reuse of existingmobile station (MS) platforms.

Moreover, highly efficient Fast Fourier Transforms (FFT's) also decreasethe power consumption in the MS. For example, at the normal symbol rateN=142=116+26=2×71 (71 is a prime number) is not a highly compositenumber.

Hence there exists a need to reduce the above problems and to provide amore efficient method for transmitting signals in a GSM system. Inparticular when the signals are precoded.

SUMMARY

It is an object of the present invention to provide an improved methodand device for transmitting data in a GSM system and to address theproblems as outlined above.

This object and others are obtained by the method and device asdescribed herein.

Thus, as realized by the inventors, one of the first tasks performed ina typical receiver for precoded EGPRS is Cyclic Prefix (CP) removal.However, since a significant amount of intersymbol interference (ISI) isintroduced already at the transmitter, it is possible to modify a partof the CP in the transmitter, after having performed pulse shaping,without incurring any loss of link performance. In accordance withembodiments described herein a shortened precoded EGPRS burst isprovided. In accordance with one embodiment the burst shortening isperformed while preserving the spectral characteristics of the signal.

In accordance with one embodiment a method of transmitting a burst ofsignals in a cellular radio system supporting data transmission usingEGPRS/EGPRS2 is provided. The method comprises providing additionalsymbols in the EGPRS/EGPRS2 burst thereby forming a long burst, andpulse shaping the long burst to forming a long baseband signal whoseduration exceeds the duration of one EGPRS/EGPRS2 time slot. The longbaseband signal is then shortened to a shortened burst having theduration of an EGPRS/EGPRS2 time slot wherein the shortened burstfulfills the same spectrum mask requirement as the EGPRS/EGPRS2 burst,and which can be transmitted as a conventional EGPRS/EGPRS2 burst.

In accordance with one embodiment the burst length of the long burst isset to 144 symbols.

In accordance with one embodiment the transmitted symbols are precoded.

In accordance with one embodiment the additional symbols are payloadand/or training symbols.

In accordance with one embodiment the shortened burst is generated bytruncation of said long baseband signal followed by multiplication by awindow function.

Thus, a long burst containing more payload or training symbols than anEGPRS/EGPRS2 burst is shortened to the same length as an EGPRS/EGPRS2burst and fulfill the same spectrum mask requirements. The additionalsymbols can be used to increase throughput (more data symbols), improvelink performance (more training symbols or lower code rates), or forother purposes such as Peak to Average Power Ratio (PAPR) reduction.

Moreover, longer bursts can be set to a highly composite sizes for theIFFT/FFT if precoding is used, which has benefits in terms of processingpower and power consumption. For example the burst length can be set to144 symbols.

In summary, burst shortening alleviates the problems with precodedEGPRS/EGPRS2 presented above while preserving backward compatibilitywith EGPRS/EGPRS2, and without any losses in link performance.

In accordance with one embodiment of transmitting signals in a GSMsystem with precoded EGPRS signals bursts, the precoded EGPRS signalbursts are shortened.

Embodiments herein also extend to a device adapted to transmit signalsin accordance with the above. The device can typically be implemented ina module comprising a micro controller or a micro processor operating ona set of computer program instructions stored in a memory, whichinstructions when executed by the module causes the module to performpower control in accordance with the method as described above. Inparticular the module can comprise controller circuitry for performingthe above methods. The controller(s) can be implemented using suitablehardware and or software. The hardware can comprise one or manyprocessors that can be arranged to execute software stored in a readablestorage media. The processor(s) can be implemented by a single dedicatedprocessor, by a single shared processor, or by a plurality of individualprocessors, some of which may be shared or distributed. Moreover, aprocessor or may include, without limitation, digital signal processor(DSP) hardware, ASIC hardware, read only memory (ROM), random accessmemory (RAM), and/or other storage media.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way ofnon-limiting examples and with reference to the accompanying drawings,in which:

FIG. 1 is a high level view of a transmitter for precoded EGPRS/EGPRS2,

FIG. 2 is a flow chart illustrating some steps performed whentransmitting a burst of EGPRS/EGPRS2 symbols,

FIG. 3 is a view of a transmitter,

FIG. 4 is a flow chart illustrating some steps performed whentransmitting a burst of EGPRS/EGPRS2 symbols,

FIG. 5 depicts a spectrum mask, and

FIGS. 6 and 7 depict left and right portions of the power vs. time mask.

DETAILED DESCRIPTION

For simplicity, the below examples consider burst formats of the form(4) without tail symbols. However, the invention is not limited to suchan embodiment but is equally applicable to other formats.

FIG. 2 is a flow chart illustrating some steps performed whentransmitting a burst of EGPRS/EGPRS2 symbols. In accordance with FIG. 2first, in a step 201 additional symbols are added to a (conventional)EGPRS/EGPRS2 burst thereby forming a long burst. Next, in a step 203 thelong burst is pulse shaped thereby forming a long baseband signal whoseduration exceeds the duration of one EGPRS/EGPRS2 time slot. Next, in astep 205, the long baseband signal is shortened to a shortened bursthaving the duration of an EGPRS/EGPRS2 time slot wherein the shortenedburst fulfills the same spectrum mask requirement as the EGPRS/EGPRS2burst, The shortened burst is then transmitted in a step 207.

In FIG. 3 a transmitter 300 that can be used for transmitting bursts ofdata in accordance with the methods described herein is depicted. Thetransmitter 300 comprises controller circuitry 301 for performing theabove methods. The controller(s) can be implemented using suitablehardware and or software. The hardware can comprise one or manyprocessors that can be arranged to execute software stored in a readablestorage media. The processor(s) can be implemented by a single dedicatedprocessor, by a single shared processor, or by a plurality of individualprocessors, some of which may be shared or distributed. Moreover, aprocessor or may include, without limitation, digital signal processor(DSP) hardware, ASIC hardware, read only memory (ROM), random accessmemory (RAM), and/or other storage media.

A detailed implementation example will now be given, which isillustrated in FIG. 4. To begin, choose a positive integer λ≦L andenlarge the burst by λ symbols, step 401. These symbols can be eitherpayload, pilots or have some other use such as PAPR reduction.Specifically, the vector of payload plus data is enlarged, step 403.

{right arrow over (z)}=[z₁ , . . . , z _(N+λ)]^(T)  (6)

The new symbols need not be added at the end, they can be placedanywhere in the burst. Next, the vector {right arrow over (z)} isprecoded, step 405.

{right arrow over (Z)}=(^(N+λ) W)^(H)·{right arrow over (z)}  (7)

Note that the new size of the Fourier transform is N+λ. After precoding,a cyclic prefix of length L is added, step 407 and step 409.

$\begin{matrix}{\left\lbrack {Z_{1}^{P},\ldots \mspace{14mu},Z_{N + L + \lambda}^{P}} \right\rbrack \overset{def}{=}{\left\lbrack {Z_{N - L + \lambda},Z_{N - L + \lambda + 1},\ldots \mspace{14mu},Z_{N + \lambda},Z_{1},Z_{2},\ldots \mspace{14mu},Z_{N + \lambda}} \right\rbrack.}} & (8)\end{matrix}$

Guard symbols are added to the left and right of (7), step 415.

$\begin{matrix}{\left\lbrack {d_{1}, d_{2}, \ldots \mspace{14mu}, d_{K + \lambda}} \right\rbrack \overset{def}{=}{\left\lbrack {\underset{\underset{guard}{}}{g_{1},\ldots \mspace{14mu},g_{\xi}}, \underset{\underset{{CP} + {payload} + {pilots}}{}}{Z_{1}^{P},Z_{2}^{P},\ldots \mspace{14mu},Z_{N + L + \lambda}^{P}}, \underset{\underset{guard}{}}{g_{\xi + 1},\ldots \mspace{14mu},g_{\eta}}} \right\rbrack .}} & (9)\end{matrix}$

A good choice for the guard symbols can be made by picking them so thatthe signal generated after pulse shaping has approximately constantamplitude over the guard. For example, if the pulse shaping filter isthe linearized Gaussian Minimum Shift Keying (GMSK) filter, then theguard symbols may be defined by, step 413.

$\begin{matrix}{{g_{m} = {A_{l}^{j\frac{\pi}{2}m}}},{1 \leq m \leq \xi},} & (10) \\{{g_{m} = {A_{r}^{j\frac{\pi}{2}{({m - \xi})}}}},{{\xi + 1} \leq m \leq {\eta.}}} & (11)\end{matrix}$

The positive real numbers A_(l), A_(r) are the amplitudes of the leftand right guard symbols step 411. These amplitudes can be adjusted tocontrol the power of the signal during ramp up or ramp down.

The signal (9) is pulse shaped, step 417 using the filter ρ.

$\begin{matrix}{{{y(t)} = {\sum\limits_{n}{d_{n} \cdot {p\left( {t - {nT} + \phi} \right)}}}},{0 \leq t \leq {\tau + {\lambda \; {T.}}}}} & (12)\end{matrix}$

Note that the signal (12) is λT seconds longer than the signal (5).

Below a description, step 419, is given how to shorten (12) so that

1. It has the same length τ as (5),

2. It fulfils the same spectrum constraints as (5), and

3. The link performance is not degraded.

Firstly, the constant λ is chosen in such a way that the time dispersioninduced by the multipath propagation radio channel (i.e. from transmitantenna to receive antenna) plus the time dispersion caused by thereceive chain is less than (L−λ+1)·T seconds.

Secondly, the first λT seconds of (12) are erased.

y _(λ)(t)=y(t+λT), 0≦t≦τ  (13)

Thirdly, two raised cosine ramp functions are defined, step 421.

$\begin{matrix}{{r_{\beta}^{l}(t)} = \left\{ \begin{matrix}{{\frac{1}{2}\left( {1 + {\cos \left( {\pi \frac{\left( {{\beta \; T} - t} \right)}{\beta \; T}} \right)}} \right)},} & {{{if}\mspace{14mu} 0} \leq t \leq {\beta \; T}} \\{1,} & {{{if}\mspace{14mu} t} \geq {\beta \; {T.}}}\end{matrix} \right.} & (14)\end{matrix}$

The parameter β determines the duration of the ramping period.

$\begin{matrix}{{r_{\beta}^{r}(t)} = \left\{ \begin{matrix}{{\frac{1}{2}\left( {1 + {\cos \left( {\pi \frac{\left( {t - \tau + {\beta \; T}} \right)}{\beta \; T}} \right)}} \right)},} & {{{{if}\mspace{14mu} \tau} - {\beta \; T}} \leq t \leq \tau} \\{1,} & {{{if}\mspace{14mu} t} \leq {\tau - {\beta \; {T.}}}}\end{matrix} \right.} & (15)\end{matrix}$

Finally, a new shortened baseband signal is generated by themultiplication of (13), (14) and (15), step 423 and 425.

s(t)=y _(λ)(t)·r _(β) ¹(t)·r _(β) ^(r)(t), 0≦t≦τ  (16)

Note that a portion of the signal S defined by (16) corresponding to λTseconds of the filtered cyclic prefix, is affected by the left ramp(14). This does not have any effect upon link performance since bydesign S is subject to a time dispersion of less than λT seconds ofHence, the received signal can still be accurately represented as acyclic convolution of the sent symbols with a channel filter. This is aproperty that allows easy demodulation by means of the DFT, and itexplains why the shortened signal (16) does not suffer from degradedperformance. Moreover, the spectrum of the product of the ramps (14) and(15) is easily obtained from the usual raised cosine spectrum and itsimpulse response, see Digital Communications, J. Proakis, Mc Graw Hill4^(th) Ed. (2000), but interchanging the time and frequency domains.Indeed, the product r_(β) ^(l)(t)·r_(β) ^(r)(t) defines a raised cosinewindow in the time domain, while the usual definition gives the raisedcosine window in the frequency domain, see Digital Communications, J.Proakis, Mc Graw Hill 4^(th) Ed. (2000). Thus, the spectrum of r_(β)^(l)(t)·r_(β) ^(r)(t) is a modified sinc function, see DigitalCommunications, J. Proakis, Mc Graw Hill 4^(th) Ed. (2000) and themagnitude of its side lobes is controlled by the roll off β. Since thespectrum of s is given by the circular convolution of the frequencyresponse of the 3 terms

y_(λ)(t), r_(β) ^(l)(t) and r_(β) ^(r)(t )  (17)

will satisfy the same spectral mask requirements as (5) provided β islarge enough. Observe that since the ramps have the value 0 for t<0 ort>τ+λT, the signal (12) can be extended to t<0 or t>τ+λT withoutaffecting the burst shortening method. This can be useful in order toensure that the spectrum of (12) is as narrow as possible and that thehigh frequency components decay as fast as possible. It is also clearfrom the description above that the raised cosine ramps (14) and (15)can be replaced by other ramping functions provided the spectrum of theshortened signal (16) satisfies the same spectrum mask requirements as(5).

An exemplary burst shortening method is depicted in FIG. 4, whichillustrates some procedural steps in accordance with the methoddescribed above Table 1 gives an example of typical parameter valuesthat can be used in an embodiment of the invention which is backwardscompatible with EGPRS/EGPRS2 at the normal symbol rate.

TABLE 1 Parameter Values Parameter Value λ 2 η 8 ξ 4 β 4 T 48/13 μs(Normal Symbol Rate) N 142 (=26 training + 116 payload) τ 577 μs L 6A_(l) 1 A_(r) 0.5

The size of the Fourier transform is N+λ=144=2⁴×3², which is a highlycomposite number. An IFFT of size 144=2⁴×3² is typically 3 to 10 timesfaster than an IFFT of N=142, depending on hardware capabilities andimplementation details.

The amount of time dispersion due to multipath radio propagation andreceive filtering that can be effectively compensated is 5T=18.5 μs.With these values of the parameters the spectrum mask requirement fornormal symbol rate, see 3GPP TS 45.005 Radio Transmission and Receptionis fulfilled. This is depicted in FIG. 5, which shows the spectrum of ashortened, IDFT precoded burst and a spectrum mask requirement inaccordance with 3GPP TS 45.005 Radio Transmission and Reception.

The left and right portions of the power vs. time mask, see 3GPP TS45.005 Radio Transmission and Reception, together with simulatedshortened bursts, are shown in FIGS. 6 and 7, respectively.

Thus, FIG. 6 shows burst power vs. time for shortened, IDFT precodedbursts. Also shown is the left part of power vs. time mask in accordancewith 3GPP TS 45.005 Radio Transmission and Reception.

Further FIG. 7 illustrates power vs. time for shortened, IDFT precodedbursts. Also shown is the right part of power vs. time mask inaccordance with 3GPP TS 45.005 Radio Transmission and Reception

This shows that the output power does not exceed the maximum allowedpower during ramping up or ramping down according to the power vs. timemask as set out in 3GPP TS 45.005 Radio Transmission and Reception.

By using the methods and devices as described herein for shortening theburst applied to EGPRS/EGPRS2, in particular a precoded EGPRS/EGPRS2burst a number of advantages compared to conventional transmission isachieved. Thus, either the payload or the training sequence (or both)can be increased, resulting in improved link performance, increasedthroughput or both. In addition it can be used to increase the length ofthe IDFT. This is beneficial because the prime factor decomposition ofthe length of the IDFT determines the computational efficiency of theIFFT. For example, an IFFT of length 142=2×71 is typically 3 to 10 timesmore complex than an IFFT of length 144=2⁴×3². Thus, a tool forsimplifying the computational burden on the precoder is provided. Thisis essential for backward compatibility with legacy base stations.Moreover a more effective FFT also saves battery and processing time inthe mobile station. In addition it is possible to preserve the spectrummask of EGPRS/EGPRS2.

1. A method of transmitting a burst of signals in a cellular radiosystem supporting data transmission using Enhanced Data rates for GSMEvolution (EGPRS)/EGPRS phase 2 (EGPRS2), the method comprising:providing additional symbols in an EGPRS/EGPRS2 burst to thereby form along burst, pulse shaping said long burst to form a long baseband signalhaving a duration that exceeds the duration of one EGPRS/EGPRS2 timeslot, shortening said long baseband signal to form a shortened burstthat has the duration of an EGPRS/EGPRS2 time slot and that fulfills thesame spectrum mask requirement as said EGPRS/EGPRS2 burst, andtransmitting the shortened burst.
 2. The method of claim 1, wherein theburst length of the long burst is set to 144 symbols.
 3. The methodaccording to claim 1, wherein the transmitted symbols are precoded. 4.The method according to claim 1, wherein the additional symbols are atleast one of payload and training symbols.
 5. The method according toclaim 1, wherein said shortening comprises truncating said long basebandsignal and then multiplying the truncated signal by a window function toform the shortened burst.
 6. A transmitter for transmitting a burst ofsignals in a cellular radio system supporting data transmission usingEnhanced Data rates for GSM Evolution (EGPRS)/EGPRS phase 2 (EGPRS2),the transmitter comprising controller circuitry configured to: provideadditional symbols in an EGPRS/EGPRS2 burst to thereby form a longburst, pulse shape said long burst to form a long baseband signal havinga duration that exceeds the duration of one EGPRS/EGPRS2 time slot,shorten said long baseband signal to form a shortened burst that has theduration of an EGPRS/EGPRS2 time slot and that fulfills the samespectrum mask requirement as said EGPRS/EGPRS2 burst, and transmit theshortened burst.
 7. The transmitter according to claim 6, wherein theburst length of the long burst is 144 symbols.
 8. The transmitteraccording to claim 6, wherein the controller circuitry is furtherconfigured to precode the symbols of the shortened burst.
 9. Thetransmitter according to claim 6, wherein the additional symbols are atleast one of payload and training symbols.
 10. The transmitter accordingto claim 6, wherein the controller circuitry is configured to shortenthe long burst by truncating the long baseband signal and thenmultiplying the trunscated signal by a window function to form theshortened burst.